Evaluation Engineeering - 13

COMMUNICATIONS TEST

SPECIAL REPORT

THE OPTICS ARE GOOD

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Vendors weigh in on developments in optical
communications technology and test solutions
By Mike Hockett, Editor-in-Chief
While 5G will undoubtedly do wonders for the massive amount of anticipated electronic devices in the next
few years, the transmission speeds of its
radio frequency-based wireless mobile
technologies are limited by the available
regulated RF spectrum.
Because of this, optical communications technology will remain a crucial
counterpart to wireless RF, as considerable advancements in optical system
capacity, network reach, and user base
size make it an attractive commercial solution. Optical wireless communication
(OWC) systems are attractive as a broadband access technology due to their high
speeds, capacity, and the cost-effectiveness of meeting bandwidth requirements
of different services and applications of
next-generation networks. Optical wireless communications can also serve as an
alternative or complementary technology
for current wireless RF solutions.
OWCs' applications range from broadband services to space missions, where
their high bandwidth capacity enables
scientists to send much more data to

Earth than possible through RF. Also,
the optical communications spectrum
has not been regulated, so those creating technology with it don't need to worry
about available allocations. Last but not
least, OWCs are considerably smaller,
lighter, and consume less power than
RF packages.
Gains in optical communications capacity come primarily from three sources:
increased spectrum efficiency via higher
modulation density, higher symbol rate,
and more carriers via techniques like
polarization and multicarrier orthogonal

frequency-division multiplexing (OFDM)
modulation.
"Testing these higher-order systems
with data rates close to 1 Tbps requires
test equipment capable of clean signal
generation and analysis and a measurement bandwidth of at least 20 GHz, to be
sure the measurements represent system
performance, not the limitations of the
test equipment," Keysight Technologies
explained in a 2017 application note.
"The instruments must offer the flexibility to address many different modulation schemes on 4 synchronized channels for a dual-polarization I/Q signal.
Traditionally, receiver tests such as phase
noise, observed signal-to-noise ratio and
polarization tests have been performed
using a 'gold' transmitter, giving a view
of the device but lacking completely deterministic knowledge."1

Keysight's M8290A Optical Modulation Analyzer and High-speed Digitizer.
SEPTEMBER 2019 EVALUATIONENGINEERING.COM

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